docs: def create_constant(self, expression, *, verbose=True):
          """Append a constant to the stored list.
  
          Parameters
          ----------
          expression : str
              Expression for the new constant.
          verbose : boolean (optional)
              Toggle talkback. Default is True
              
          See Also
          --------
          set_constants
              Remove and replace all constants.
          remove_constant
              Remove an individual constant.
          """
          if expression in self.constant_expressions:
              wt_exceptions.ObjectExistsWarning.warn(expression)
              return self.constants[self.constant_expressions.index(expression)]
          constant = Constant(self, expression)
          if constant.units is None:
              constant.convert(constant.variables[0].units)
          self._constants.append(constant)
          self.flush()
          self._on_constants_updated()
          if verbose:
              print("Constant '{}' added".format(constant.expression))
          return constant